Blood purifying device and method of operating the same

ABSTRACT

A blood purifying apparatus particularly suitable for continuous blood purification, and a method of controlling the same whereby the weight of body fluid removed from a patient and a feed weight to the patient can be more accurately controlled. A blood purifying apparatus  50  adapted for the continuous blood purification includes a drain C, a dialysate feed A, and a replacement fluid feed B, which are equipped with transfer pumps  5, 6, 7 , respectively, reservoir containers  8, 9 , and  10 , respectively, that are capable of storing a predetermined volume, and fluid level sensors  11, 12 , and  13 , respectively. The blood purifying apparatus further includes a single weightmeter  20  capable of measuring the reservoir containers  8, 9 , and  10  all at the same time.

FIELD OF THE INVENTION

The present invention relates to a blood purifying apparatus and amethod of controlling the apparatus, particularly to a blood purifyingapparatus and a method of controlling the apparatus suitable for thegenerically called continuous blood purification, such as continuoushemofiltration, continuous hemodialysis, and continuoushemodiafiltration.

BACKGROUND ART

In renal failure patients, normally urine volumes decrease due todeterioration of renal function, often resulting in overhydration. Atreatment is therefore required that would pass the blood of the patientthrough an extracorporeal circulation so that the condition of theirbody's water can be as nearly normalized as possible. This process ofremoving water from the body is referred to as “body fluid removal.”Because the total body fluid variation amount is managed based on theremoval weight of body fluid during treatment, the removal weight ofbody fluid is considered the most important parameter in patientmanagement.

In recent years, for the treatment of renal failure or multiple organfailure with serious complications in the circulatory system, thegenerically called continuous blood purification has proved effective inthe areas of emergency and intensive care. The continuous bloodpurification includes continuous hemofiltration (to be hereafterreferred to simply as CHF), continuous hemodialysis (to be hereafterreferred to simply as CHD), and continuous hemodiafiltration (to behereafter referred to simply as CHDF).

CHF is a technique whereby blood is caused to flow in a blood purifyingapparatus accommodating a semipermeable membrane in order to expel watercontaining waste products through the filtering membrane whiledelivering replacement fluid to the body continuously and slowly. CHD isa technique whereby dialysis for achieving an acid-base equilibrium byosmosis, for example, is performed continuously and slowly. CHDF is atechnique combining CHF and CHD, whereby, in order to improve the smallmolecular-weight removal performance of CHF, a dialysate is caused toflow on the filtrate side of the blood purifying device so that adialysis effect can be obtained. In any of these blood purifyingmethods, the continuous and slow treatment is characterized in that, asthe name suggests, a single treatment is conducted over several days andblood purification is carried out slowly. Such a treatment greatlydiffers from the simple hemodialysis or hemofiltration in terms oftemporal magnitude, the latter techniques requiring 4 to 5 hours for asingle treatment.

A preferable example of a blood purifying apparatus based on theaforementioned continuous blood purification is disclosed in JP PatentPublication (Kokai) No. 9-239024 A. The apparatus comprises at leasteither a means for feeding a dialysate for hemodialysis or a means forfeeding a replacement fluid for hemofiltration, a drain means, and ablood circulation path. Each of the means is equipped with a reservoircontainer, a fluid transfer pump, and a plurality of weightmeters forweighing the reservoir container. Based on the information provided byeach of the weightmeters, the flow rate of each fluid transfer pump isindividually controlled. Another example suitable for CHF or CHD isdisclosed in JP Patent Publication (Kokai) No. 4-70909 A. The examplecomprises at least either a means for feeding a dialysate forhemodialysis or a means for feeding a replacement fluid forhemofiltration, a drain means, and a blood circulation path. Each of themeans is equipped with a reservoir container and a fluid transfer pump,the reservoir container being provided with a fluid level sensor fordetecting an upper limit and a lower limit of the stored quantity of thereservoir container. The apparatus further comprises a singleweightmeter for weighing two reservoir containers all at the same time.Based on the information provided by the weightmeter, the flow rate offluid transfer pump is individually controlled.

FIG. 3 shows the concept of the blood purifying apparatus of theaforementioned first example, which is based on the continuous bloodpurification. A blood purifying apparatus 50′ is comprised of a blooddrawing line 3 and a blood retransfusing line 4, which together form ablood circulation path; a drain line 23 for draining water containingwaste products; a replacement fluid line 25 connected to the bloodretransfusing line 4 for delivery of replacement fluid to the patient;and a dialysate feeding line 24 for feeding a dialysate to the filtrateside within the blood purifying device 2. In the blood drawing line 3,there is provided a blood pump 1. A blood purifying device 2, whichincludes a filtration membrane M, is disposed between the blood drawingline 3 and the blood retransfusing line 4.

The drain line 23 includes a drain transfer pump 5 for draining afiltrate and dialysis drain fluid from the blood purifying device 2, adrain reservoir container 8 connected to a drain branch line 17 thatbranches off on the outlet side of the drain transfer pump 5; and ashutoff valve 14 attached to the drain line 23 downstream of the branchportion. The drain reservoir container 8 is equipped with a weightmeter26 for drainage weighing purposes.

The dialysate line 24 includes a transfer pump 6 for feeding a dialysateto the filtrate side within the blood purifying device 2; a dialysatereservoir container 9 connected to a dialysate branch line 18 thatbranches off on the inlet side of the dialysate transfer pump 6; and ashutoff valve 15 attached to the dialysate transfer line 24 upstream ofthe branch portion. The dialysate reservoir container 9 is equipped witha weightmeter 27 for dialysate weighing purposes.

The replacement fluid line 25 includes a transfer pump 7 for feeding areplacement fluid to the patient; a replacement fluid reservoircontainer 10 connected to a replacement branch line 19 branching off onthe inlet side of the replacement fluid transfer pump 7; and a shutoffvalve 16 attached to the replacement fluid line 25 upstream of thebranch portion. The replacement fluid reservoir container 10 is equippedwith a weightmeter 28 for weighing the replacement fluid.

The blood taken out from a patient using the blood pump 1 passes throughthe blood drawing line 3 and is then introduced into the blood purifyingdevice 2 including the filtration membrane M, where waste products orthe like are removed. In the blood purifying device 2, where a dialysateis supplied by the transfer pump 6 for dialysate, an acid-baseequilibrium, for example, is established, and the filtrate and dialysisdrain fluid are drained by the drain transfer pump 5. The blood that hasbeen subjected to filtration and dialysis in the blood purifying device2 is then returned to the patient via the blood retransfusing line 4, inthe course of which a replacement fluid of substantially an equal weightto that of the filtrate is added by the replacement fluid transfer pump7, thus delivering the replacement fluid to the patient.

The device thus does not require frequent weighing or adjustmentoperations by the staff, and is capable of continuously performingtreatment in a safe manner while appropriately controlling the bodyfluid weight of the patient. Furthermore, a dialysate reservoir unit 21or a replacement fluid reservoir unit 22 can be exchanged as needed, or,in the case where the filtrate and dialysis drain fluid are collected ina tank, the tank can be exchanged as needed, without directly affectingthe measurement of the weight of removed body fluid or withoutterminating the treatment.

The transfer pumps are associated with certain amounts of flow rateerrors. In order to minimize the influence of such errors, in theabove-described apparatus, the reservoir containers 8, 9, and 10 areequipped with the weightmeters 26, 27, and 28, respectively, so thatdata can be supplied from the individual weightmeters to a control unit,which is not shown. The control unit monitors the data from theweightmeters 26, 27, and 28 at all times, and calculates the actual flowrate based on a change in weight per unit time. If it finds a differencebetween the actual flow rate and a set flow rate, the control unitautomatically adjusts the rotation speed of a motor in each of thetransfer pumps 5, 6, and 7 individually, such that the set flow rateequals the actual flow rate so as to maintain a flow rate accuracy.

Although the above-described apparatus is capable of maintaining a highflow rate accuracy, it inevitably suffers from errors on the order of 1%in the flow rate accuracy in each transfer pump in actual operations,due to factors such as the temperature characteristics of the weightsensors and of the measurement electronic circuitry, variations withtime, methods of adjustment during manufacture, variations in the shapeof each reservoir container, and so on.

As described above, the weight of body fluid removed from a renalfailure patient ΔV(L), which is managed as an important parameter, isdetermined by the following equation:ΔV=V _(F) −V _(C) −V _(D)  (1)where V_(F) (L) is the amount of fluid drained by the drain transferpump 5, V_(C) (L) is the amount of replacement fluid supplied by thereplacement fluid transfer pump 7, and V_(D) (L) is the weight ofdialysate supplied by the dialysate feed pump 6.

Conventionally, when performing a treatment based on CHDF, the flow rateof the transfer pumps is generally on the order of 1 L/hr. For example,if the flow rate of the drain transfer pump 5 is set at 1 L/hr, that ofthe replacement fluid transfer pump 7 at 0.5 L/hr, and that of thedialysate transfer pump 6 at 0.5 L/hr, then V_(F)=24±0.24 (L),V_(C)=12±0.12 (L), and V_(D)=12±0.12 (L) in 24 hours, assuming that eachtransfer pump has a flow rate error of approximately 1%. In this case,if the removal weight of body fluid ΔV is calculated according toequation (1), ΔV=0±0.48 (L), thus indicating that the body fluid removalerror can be reduced to approximately 0.48 (L) or less, whichcorresponds to 2% of the drained volume V_(F).

DISCLOSURE OF THE INVENTION

In recent years, when performing a treatment based on CHDF or the like,in order to improve the efficiency of the treatment, the flow rate oftransfer pumps are increasingly often set at a high level, such as onthe order of 10 L/hr. In such a case, if the flow rate of the draintransfer pump 5 is set at 10 L/hr, that of the replacement fluidtransfer pump 7 at 5 L/hr, and that of the dialysate transfer pump 6 at5 L/hr in a conventional apparatus with a flow rate error on the orderof 1% in each transfer pump, then V_(F)=240±2.4 (L), V_(C)=120±1.2 (L),and V_(D)=120±1.2 (L) in 24 hours. In this case, if the removal weightof body fluid ΔV is calculated according to equation (1), ΔV=0±4.8 (L),thus indicating a body fluid removal error of as much as about 4.8 L,which corresponds to 2% of the drained volume V_(F).

When there are such large errors, a problem could arise where the bloodpurifying procedure increases the risk of the body fluid balance of thepatient becoming abnormal, rather than providing the intendedtherapeutic effect. Although in reality such a problem is prevented byperforming a mutual feedback control and the patient is subject to noadverse effects, it is nevertheless desired to minimize the body fluidremoval error without performing such a feedback control.

Thus, the inventors came to realize that there was a need for some meansfor calculating and controlling the flow rate of each transfer pump withhigh accuracy in order to manage the removal weight of body fluid moreaccurately than before in accordance with the continuous bloodpurification. In accordance with the aforementioned conventionaltechnique, however, the flow rate accuracy is maintained for eachtransfer pump. Therefore, in order to more accurately manage the removalweight of body fluid, the flow rate accuracy of each pump must beimproved to the order of 0.1%. The maximum flow rate accuracy achievableby the current technology, however, is on the order of 1%.

The blood purifying apparatus disclosed in JP Patent Publication (Kokai)No. 4-70909 A (1992) comprises one weightmeter for weighing tworeservoir containers all at the same time, wherein each transfer pump isindividually controlled on the basis of the information provided by theweightmeter. As a result, the flow rate error can be reduced to someextent as compared with the example in which two weightmeters aredisposed for each reservoir container. However, in this blood purifyingapparatus, it is necessary to combine conventional dialysis apparatuseswhen performing a hemodialysis, which leads to unsatisfactory flow rateaccuracy in the removal weight of body fluid and to a complicatedstructure of the system. Hence, there is a need for furtherimprovements.

In view of the aforementioned problems of the prior art, it is thereforean object of the invention to provide a blood purifying apparatusparticularly suitable for the continuous blood purification, and amethod of controlling the same, whereby, upon treatment of a renaldisease or multiple organ failure patient, the removal weight of bodyfluid in the patient as well as the transfer volume to the patient canbe more accurately managed.

In order to achieve the aforementioned object, the invention providesthe following:

-   1. A blood purifying apparatus 50 comprising a dialysate feed means    A, a replacement fluid feed means B, a drain means C, a blood    purifying device 2, and a blood circulation path consisting of a    blood drawing line 3 and a blood retransfusing line 4, wherein:

said dialysate feed means A comprises: a dialysate transfer line 24 ofwhich one end is connected to said blood purifying device 2 and theother end connected to a dialysate reservoir unit 21; a dialysatetransfer pump 6 disposed in the line; a dialysate reservoir container 9connected to a dialysate branch line 18 branching off on an inlet sideof said dialysate transfer pump 6; and a shutoff valve 15 attached tosaid dialysate transfer line upstream of a branch portion;

said replacement fluid feed means B comprises: a replacement fluid feedline 25 of which one end is connected to said blood retransfusing line 4and the other end connected to a replacement fluid reservoir unit 22; areplacement fluid transfer pump 7 disposed in the line; a replacementfluid reservoir container 10 connected to a replacement fluid branchline 19 branching off on an inlet side of said replacement fluidtransfer pump 7; and a shutoff valve 16 attached to said replacementfluid line 25 upstream of a branch portion;

said drain means C comprises: a drain line 23 of which one end isconnected to said blood purifying device 2 and the other end opened; adrain transfer pump 5 disposed in the line; a drain reservoir container8 connected to a drain branch line 17 branching off from an outlet sideof said drain transfer pump 5; and a shutoff valve 14 attached to saiddrain line 23 downstream of a branch portion,

wherein the three reservoir containers 8, 9, and 10 are equipped withfluid level sensors 11, 12, and 13, said apparatus further comprising aweightmeter 20 for weighing the said three reservoir containers 8, 9,and 10 all at the same time, and a control unit 30 for controlling theopening and closing of said shutoff valves 14, 15, and 16, and the pumpflow rate of each of said transfer pumps 6, 7, and 5.

-   2. The aforementioned blood purifying apparatus, wherein the    individual fluid level sensors 11, 12, and 13 detect an upper limit    of a fluid in each of said reservoir containers 8, 9, and 10.-   3. The aforementioned blood purifying apparatus, wherein the fluid    level sensor 11 for said drain reservoir container 8 detects a lower    limit of a fluid in said drain reservoir container 8, and the fluid    level sensors 12 and 13 for said dialysate reservoir container and    the replacement fluid reservoir container detect an upper limit of    fluids in said dialysate reservoir container 9 and the replacement    fluid reservoir container 10.-   4. The aforementioned blood purifying apparatus, wherein said    apparatus is of a continuous and slow type.

In order to achieve the objective, the invention further provides:

-   5. A method of controlling the aforementioned blood purifying    apparatus, said method comprising performing a removed body fluid    weight measuring phase consisting of:

a first phase in which the shutoff valves 15, 16, and 17 are opened,whereby said dialysate reservoir container 9 and said replacement fluidreservoir container 10 are each filled with a fluid while at the sametime a fluid is discharged from said drain reservoir container 8; and

a second phase in which said apparatus is controlled with each of saidshutoff valves 15, 16, and 17 closed, and a change in the total fluidweight in said dialysate reservoir container 9, said replacement fluidreservoir container 10, and said drain reservoir container 8 during theoperation of said apparatus is acquired from information provided bysaid weightmeter 20 in order to weigh the removal weight of body fluid,

wherein said control unit 30 controls the flow rate of the transferpumps 6, 7, and 5 such that a desired removal weight of body fluid canbe obtained in said second phase.

-   6. A method of controlling the aforementioned blood purifying    apparatus, said method comprising performing a feed weight measuring    phase consisting of:

a third phase in which each of said shutoff valves 15, 16, and 17 isopened whereby said dialysate reservoir container 9 and said replacementfluid reservoir container 10 are filled with individual fluids while atthe same time a fluid is discharged from said drain reservoir container8; and

a fourth phase in which said apparatus is controlled with only theshutoff valve 15 for said dialysate feed means A and the shutoff valve16 for said replacement fluid feed means B closed, and in which a changein the total fluid weight in said dialysate reservoir container 9, saidreplacement fluid reservoir container 10, and said drain reservoircontainer 8 is acquired from information provided by said weightmeter 20so as to calculate a feed weight which is the sum of the weight ofreplacement fluid and the weight of the dialysate,

wherein:

said control unit 30 controls the flow rate of the dialysate transferpumps 6, 7, and 5 such that a desired feed weight can be obtained duringthe fourth phase.

-   7. A method of controlling the aforementioned blood purifying    apparatus, said method comprising an arbitrary combination of the    operation method based on said removed body fluid weight measuring    phase and the operation method based on said feed weight measuring    phase.-   8. The aforementioned blood purifying apparatus operation method,    said method comprising alternately repeating the operation method    based on the removed body fluid weight measuring phase and the    operation method based on the feed weight measuring phase.

Thus, in the blood purifying apparatus and methods of controlling thesame in accordance with the invention, the individual reservoircontainers (the dialysate reservoir container 9, the replacement fluidreservoir container 10, and the drain reservoir container 8) are weighedby a single weightmeter all at the same time, thereby making it possibleto reduce the error in the removal weight of body fluid to the order of0.2% of the drain fluid weight, as will be described later. This is asignificant improvement as compared with the conventional apparatuses ofthe type whereby each reservoir container is measured individually,where the error can be reduced only to about 2% or so of the drain fluidweight. The error in the feed weight can also be maintained at the samelevel as that in the conventional apparatuses. Furthermore, since theapparatus of the invention employs only one weightmeter, the overallcost, including that of the control unit, can be significantly reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows an embodiment of the blood purifyingapparatus according to the invention.

FIG. 2 schematically shows another embodiment of the blood purifyingapparatus of the invention.

FIG. 3 schematically shows an example of a conventional blood purifyingapparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

A blood purifying apparatus of the invention will be hereafter describedwith reference made to the accompanying drawings. FIG. 1 schematicallyshows an embodiment of the blood purifying apparatus of the invention.Apparatus 50 is basically the same as the apparatus shown in FIG. 3.Namely, the apparatus 50 is adapted for the continuous hemodiafiltration(CHDF) method combining continuous hemofiltration (CHF) and continuoushemodialysis (CHD). In FIG. 1, constituent members with the samefunctions as those of the constituent members shown in FIG. 3 areidentified by similar reference characters.

As in the conventional apparatus shown in FIG. 3, the blood purifyingapparatus 50 is comprised of a blood drawing line 3 and a bloodretransfusing line 4 constituting a blood circulation path; a drainmeans C for discharging water containing waste products, for example;replacement fluid feed means B connected to the blood retransfusing line4 for injecting a replacement fluid to the patient; and a dialysate feedmeans A for feeding a dialysate to the filtrate side within a bloodpurifying device 2. In the blood drawing line 3, there is provided ablood pump 1, and between the blood drawing line 3 and the bloodretransfusing line 4, there is disposed the blood purifying device 2accommodating a filtration membrane M.

The drain means C is a means for discharging a filtrate and dialysisdrain fluid from the blood purifying device 2. The drain means Cincludes a drain line 23 with one end connected to the blood purifyingdevice 2 and the other end opened; a drain transfer pump 5 disposed inthe line; a drain reservoir container 8 connected to a drain branch line17 branching off from the drain line on the outlet side of the draintransfer pump 5; and a shutoff valve 14 attached to the drain line 23downstream of the branching portion. The drain reservoir container 8 isequipped with a fluid level sensor 11 for detecting the filled quantityin the drain reservoir container 8. The drain transfer pump 5 dischargesa filtrate in the case where the present apparatus is used for CHF, or adialysate in the case where CHD is employed.

The dialysate feed means A is a means of feeding a dialysate to thefiltrate side within the blood purifying device 2. It includes adialysate transfer line 24 of which one end is connected to the bloodpurifying device 2 and the other end connected to a dialysate reservoirunit 21; a dialysate transfer pump 6 disposed in the line; a dialysatereservoir container 9 connected to a dialysate branch line 18 branchingoff on the inlet side of the dialysate transfer pump 6; and a shutoffvalve 15 attached to the dialysate transfer line 24 upstream of thebranching portion. The dialysate reservoir container 9 is also equippedwith a fluid level sensor 12 for detecting the filled quantity in thedialysate reservoir container 9. While the dialysate transfer pump 6operates to deliver a dialysate to the filtrate side within the bloodpurifying device 2 when the apparatus is used for CHD, the pump isturned off when the apparatus is used for CHF.

The replacement fluid feed means B is a means of feeding a replacementfluid to the patient, and it includes a replacement fluid line 25 ofwhich one end is connected to the blood retransfusing line 4 and theother end connected to a replacement fluid reservoir unit 22; areplacement fluid transfer pump 7 disposed in the line; a replacementfluid reservoir container 10 connected to a replacement fluid branchline 19 branching off at an inlet side of the replacement fluid transferpump 7; and a shutoff valve 16 attached to the replacement fluid line 25upstream of the branching portion. The replacement fluid reservoircontainer 10 is also equipped with a fluid level sensor 13 for detectingthe filled quantity in the replacement fluid reservoir container 10.Although the replacement fluid transfer pump 7 is operated to feed areplacement fluid to the blood supplied from the blood purifying device2 even when the present apparatus is used for CHF, the pump is turnedoff when CHD is employed.

As described above, the reservoir containers 8, 9, and 10 of theinvention are equipped with the fluid level sensors 11, 12, and 13,respectively. The fluid level sensors 11, 12, and 13, which detect achange in the level of the reservoir containers 8, 9, and 10,respectively, are not particularly limited in terms of their detectionprinciple. Thus, they may be comprised of any of the known components,such as float switches, photoelectric sensors, ultrasound-transmittingbubble detectors, or capacitance-type proximity sensors, for example.

Preferably, the fluid level sensors 11, 12, and 13 detect an upper limitof the level in the reservoir containers 8, 9, and 10, respectively, soas to prevent an overflow, and they are mounted on an upper part of thereservoir containers 8, 9, and 10, respectively. This is because theweighing is carried out by raising or lowering the fluid level in eachof the reservoir containers 8, 9, and 10 to a certain level. If thefluid level sensors were to be disposed each at an upper and a lowerportion of the reservoir container, and if the fluid level sensors wereto be used at the beginning and end of the weighing, the rate of changeof the level would vary depending on the flow rate, resulting in a largedifference in a single-weighing time between a high flow rate and a lowflow rate. As a result, response would be slower in the case of a lowflow rate where the weighing time would be longer, and the measurementaccuracy would drop in the case of a high flow rate where the weighingtime would be shorter. Thus, an upper limit of the level is mechanicallydetected by the fluid level sensors 11, 12, and 13, and, as regards thelower limit, a reduction amount or a reduction time of the fluid may beset in advance in accordance with the flow rate at the time of use.Alternatively, a reduction rate of the fluid may be set in advance byalso taking into consideration the capacity of the reservoir container.In this way, the apparatus can handle any flow rate without moving theposition of the fluid level sensor or changing the capacity of thereservoir containers, which is particularly suitable for the continuousand slow treatment method that involves a wide range of flow rates fromsmall to large flow rates. It should be noted, however, that the fluidlevel sensor attached to the drain reservoir container 8 may preferablybe adapted to detect a lower limit of the level, as will be describedlater.

As in the apparatus shown in FIG. 3, the blood taken out of the patientby the blood pump 1 passes through the blood drawing line 3 and is thenintroduced into the blood purifying device 2 accommodating thefiltration membrane M, where waste products or the like are removed. Inthe blood purifying device 2, a dialysate is supplied by the dialysatetransfer pump 6 and an acid-base equilibrium is achieved by osmosis, forexample. The filtrate and dialysis drain fluid are discharged by thedrain transfer pump 5. To the blood that has been subjected tofiltration and dialysis in the blood purifying device 2, a replacementfluid of substantially the same quantity as that of the aforementionedfiltrate is added by the replacement fluid transfer pump 7 as the bloodis transported back to the patient via the blood retransfusing line 4,thereby injecting the replacement fluid to the patient.

The blood purifying apparatus 50 of the present embodiment includes aweightmeter 20 that weighs the individual reservoir containers, namelythe drain reservoir container 8, the dialysate reservoir container 9,and the replacement fluid reservoir container 10, all at the same time.The weightmeter 20 is produced in accordance with the following designcriteria. Namely, any of the values obtained (W₈−W₉)/W, (W₈−W₁₀)/W, and(W₉−W₁₀)/W is a small value on the order of 1/1000, for example, whereW₈(g) is the measurement value of the weightmeter 20 when a fluid ofW(g) is put in the drain reservoir container 8 while emptying thedialysate reservoir container 9 and the replacement fluid reservoircontainer 10, W₉(g) is the measurement value of the weightmeter 20 whena fluid of W(g) is put in the dialysate reservoir container 9 whileemptying the drain reservoir container 8 and the replacement fluidreservoir container 10, and W₁₀(g) is the measurement value of theweightmeter 20 when a fluid of W(g) is put in the replacement fluidreservoir container 10 while emptying the drain reservoir container 8and the dialysate reservoir container 9. The error with respect to theactual weight, such as (W−W₈)/W, (W−W₉)/W, or (W−W₁₀)/W, maysufficiently be about 5/100 or smaller. In other words, although themost important thing is not to have variations in the measurement valueregardless of in which of the reservoir containers 8, 9, and 10 thefluid is put, the values of (W₈−W₉)/W, (W₈−W₁₀)/W, and (W₉−W₁₀)/W can bemade about 1/1000 or smaller because all of the reservoir containers 8,9, and 10 are measured by the same weightmeter 20.

Hereafter, the operation of the blood purifying apparatus 50 isdescribed. The operation includes a “removed body fluid weight measuringphase” consisting of a first and a second phase, and a “feed weightmeasuring phase” consisting of a third and a fourth phase, the variousphases being appropriately combined when the apparatus 50 is controlled.

In the first phase, the shutoff valves 14, 15, and 16 are opened, andthe blood pump 1 and the individual transfer pumps 5, 6, and 7 areoperated with a set flow rate. As a result, the filtrate that hasremained in the drain reservoir container 8 is discharged via the drainbranch line 17 and the line 23 due to the drop. To the dialysatereservoir container 9 and the replacement fluid reservoir container 10,there are poured the dialysate and the replacement fluid from thedialysate reservoir unit 21 and the replacement fluid reservoir unit 22,respectively, due to the drop, via the dialysate branch line 18 and thereplacement fluid branch line 19, respectively.

When the fluid level sensor 12 detects that a predetermined amount hasbeen poured into the dialysate reservoir container 9, a detection signalis supplied to a control unit 30. Thereafter, the opening and closing ofthe shutoff valve 15 is repeated so as to maintain the fluid weight inthe dialysate reservoir container 9. Similarly, when the fluid levelsensor 13 detects the end of pouring of a predetermined amount in thereplacement fluid reservoir container 10, a detection signal is suppliedto the control unit 30, and thereafter the opening and closing of theshutoff valve 16 is repeated so as to maintain the fluid weight in thereplacement fluid reservoir container 10. After the fluid level sensors12 and 13 thus detect the completion of the filling of the reservoircontainers 9 and 10, the shutoff valve 14 is opened for a certainduration of time, thereby completing the first phase and transitioningto the second phase.

In the second phase, the individual valves 14, 15, and 16 are closed,and then a drain fluid is poured into the drain reservoir container 8 inaccordance with the flow rate of the drain transfer pump 5. On the otherhand, the fluids in the dialysate reservoir container 9 and thereplacement fluid reservoir container 10 are discharged in accordancewith the flow rate of the transfer pumps 6 and 7, respectively.

When the completion of pouring of the fluid in the drain reservoircontainer 8 is detected by the fluid level sensor 11, the second phaseis terminated. Alternatively, the second phase may be terminated when:the fluid in the drain reservoir container 8 has reached a predeterminedratio of the weight upon completion of the filling, such as 70% or more,as calculated on the basis of the set flow rate of the transfer pump 5;when the fluid in the dialysate reservoir container 9 has dropped belowa predetermined ratio of the weight upon completion of the filling, suchas 30% or less, as calculated on the basis of the set flow rate of thetransfer pump 6; or when the fluid in the replacement fluid reservoircontainer 10 has dropped below a predetermined ratio of the weight uponcompletion of the filling, such as 30% or less, as calculated on thebasis of the set flow rate of the transfer pump 7. The former, i.e., thecontrol of the second phase based on level detection, is preferable onlywhen the set range of the flow rate of the transfer pumps is narrow fornormal dialysis or filtration, for example. The latter, i.e., thecontrol of the phase based on a set value, is particularly preferablewhen the set range of the flow rate of the transfer pumps is wide forCHF, CHD, and CHDF treatment, for example, such as when the range is0.01 L/Hr to 12 L/Hr.

When the measurement time between the start to the end of the secondphase is ΔT (sec), the actual flow rate of the drain transfer pump 5 isQ_(f) (L/sec), the actual flow rate of the dialysate transfer pump 6 isQ_(d), and the actual flow rate of the replacement fluid transfer pump 7is Q_(r), the weight of drain fluid in the drain fluid reservoircontainer 8 increases by ΔT×Q_(f) in the measurement time, the weight ofdialysate in the dialysate reservoir container 9 decreases by ΔT×Q_(d),and the replacement fluid in the replacement fluid reservoir container10 decreases by ΔT×Q_(r). Thus, when the amount of change in the totalweight of the individual reservoir containers 8, 9, and 10 is ΔW,ΔW=ΔT×(Q_(f)−Q_(r)−Q_(d)), which is the removal weight of body fluid inthe second phase. By measuring ΔW with the weightmeter 20, the removalweight of body fluid can be accurately measured.

By automatically repeating the cycle consisting of the first phase,which is a weighing-preparation step, and the second phase (“removedbody fluid weight measuring phase”), in which the removal weight of bodyfluid is measured, the removal weight of body fluid can beintermittently measured in an accurate manner.

Further, in accordance with the invention, the “feed weight measuringphase” consisting of the third and fourth phases is used in combinationwith the aforementioned “body fluid removal weight weighing phase.” Inthis way, the feed weight, which is the sum of the weights of thereplacement fluid and the dialysate, can be measured, in addition to themeasurement of the removal weight of body fluid.

The third phase proceeds in the same way as the first phase, and it endswhen the fluid level sensors 12 and 13 detect the end of the filling ofthe reservoir containers 8 and 9 and the shutoff valve 14 is opened fora certain duration of time.

In the fourth phase, the shutoff valve 14 is opened while the shutoffvalves 15 and 16 are closed. When the shutoff valve 14 is open, no fluidenters the drain reservoir container 8. On the other hand, when theshutoff valves 15 and 16 are closed, the fluids in the dialysatereservoir container 9 and the replacement fluid reservoir container 10are discharged in accordance with the flow rate of the transfer pumps 6and 7, respectively. The fourth phase is terminated when the fluid inthe dialysate reservoir container 9 or the replacement fluid reservoircontainer 10 dropped below a predetermined ratio of the weight at theend of filling, such as 30% or less, as calculated from the set flowrate of the transfer pumps 6 and 7.

When the measurement time between the start to the end of the fourthphase is ΔT (sec), the actual flow rate of the dialysate transfer pump 6is Q_(d) and the actual flow rate of the replacement fluid transfer pump7 is Q_(r), the weight of drain fluid in the drain fluid reservoircontainer 8 does not change at all in the measurement time, while theweight of dialysate in the dialysate reservoir container 9 decreases byΔT×Q_(d) and that of the replacement fluid in the replacement fluidreservoir container 10 decreases by ΔT×Q_(r). When the amount of changein the total weight of the individual reservoir containers 8, 9, and 10is ΔW, ΔW=ΔT×(0−Q_(r)−Q_(d)), or ΔT×(Q_(r)+Q_(d)), which is −ΔW. Thus,−ΔW is the “replacement fluid weight+dialysate weight” in the fourthphase. By measuring −ΔW with the weightmeter 20, the “replacement fluidweight+dialysate weight” (the feed weight) can be accurately measured.

Thus, a single cycle consists of the third phase, which is the weighingpreparation step, followed by the fourth phase, in which the“replacement fluid weight+dialysate weight” is measured. This cycle isreferred to as the “feed weight measuring phase.” By automaticallyrepeating the cycle, the feed weight can be intermittently measured inan accurate manner.

During the transition from the first to the second phase (or from thethird to the fourth phase), another embodiment may be adopted, as willbe described below with reference made to FIG. 2. In this embodiment,although the fluid level sensors 12 and 13 for the dialysate reservoircontainer 9 and the replacement fluid reservoir container 10 are eachattached to an upper portion of the reservoir containers 9 and 10,respectively, the fluid level sensor 11 for the drain reservoircontainer 8 is attached to the drain branch line 17 so as to detect thatthe drain reservoir container 8 is completely empty. Alternatively, thefluid level sensor 11 may be attached to a lower portion of the drainreservoir container 8, though not shown, so as to detect a lower limitthereof.

In this embodiment, the apparatus is controlled in the same manner asdescribed with reference to FIG. 1 until the fluid level sensors 12 and13 for the dialysate reservoir container 9 and the replacement fluidreservoir container 10 detect that the respective containers have beenfilled to a predetermined amount in the first phase. When the fluidlevel sensor 11 attached to the drain reservoir container 8 detects alower limit level, the first phase is presumed to have ended, thereaftermoving to the above-described second phase. In the second phase andafterwards, the removal weight of body fluid is weighed in the samemanner as in the case of the apparatus shown in FIG. 1. The sameprocedure may be adopted during the transition from the third phase tothe fourth phase. In this way, it can be known whether the fluidcollected in the drain reservoir container 8 has been completelydischarged, so that the time of the first phase can be advantageouslyreduced.

In an actual operation of the apparatus of the invention, by combiningthe “removed body fluid weight measuring phase” and the “feed weightmeasuring phase,” a more accurate delivery management can be performed.The combination of the two phases is not particularly limited, and sothey may be combined in any desired manner. Thus, a sequence may beselected from a variety of combinations depending on the objective andthe state of operation of the apparatus. For example, the sequence mayconsist of an alternate repetition of the “removed body fluid weightmeasuring phase” and the “feed weight measuring phase”; it may consistof one phase continued and then followed by the other phase; or it maybe completely randomized. In a specific example, the “removed-waterweighing phase” may be repeated in the early stages of operation, andthe “feed weight measuring phase” may take part somewhere along thesequence. In another example, the “removed body fluid weight measuringphase” and the “feed weight measuring phase” may comprise the sequenceat the ratio of 3 to 1. However, a sequence is preferably such that the“removed body fluid weight measuring phase” and the “feed weightmeasuring phase” are alternately repeated, as this would enable theremoval weight of body fluid and the feed weight to be corrected at thesame proportions and because the phases can be easily set.

In accordance with the invention, the manner of controlling the valvesor the like is not limited to the above descriptions, and it is onlynecessary that the amount of change in the total weight of the reservoircontainers 8, 9, and 10 can be measured by the weightmeter 20 all at thesame time in the second and the fourth phase.

Furthermore, in the blood purifying apparatus of the invention, sincethe removal weight of body fluid can be accurately weighed, the removalweight of body fluid can be accurately controlled by controlling therotation speed of at least one transfer pump such that a set removalweight of body fluid is equal to the measured removal weight of bodyfluid. For example, every time the second phase ends, a set removalweight of body fluid V_(ref) that is converted from the set flow rateand a cumulative weight V_(mes) of the measured removal weight of bodyfluids are calculated. If (V_(ref)−V_(mes)) is positive, the rotationspeed of the drain transfer pump 5 is increased, while if(V_(ref)−V_(mes)) is negative, the rotation speed of the transfer pump 5is decreased. In this way, the removal weight of body fluid can beaccurately controlled. Alternatively, instead of controlling therotation speed of the drain transfer pump 5, the flow rate may also becorrected by controlling the rotation speed of the dialysate pump 6 orthat of the drain replacement fluid transfer pump 7 to be lower orhigher.

Since the “replacement fluid weight+dialysate weight” (feed weight) canbe accurately controlled, it is also possible to correct the flow rateof the replacement fluid and the dialysate by decreasing or increasingthe rotation speed of the transfer pumps 6 and 7 such that the set flowrate and the measured flow rate coincide. Furthermore, upon correctionof the flow rates of the replacement fluid and the dialysate, by makinga correction to the drain transfer pump 5 equivalent to the correctionmade to the transfer pumps 6 and 7, the accuracy of body fluid removalthat is accurately controlled at the end of the second phase can bemaintained.

The timing of the aforementioned correction is selected such that theremoval weight of body fluid is corrected each time the second phaseends while correcting the feed weight each time the fourth phase ends,for example. This method is preferable in systems in which the “removedbody fluid weight measuring phase” is repeated at the initial stages ofoperation and thereafter the “feed weight measuring phase” is initiatedsomewhere along the sequence. Alternatively, the correction may be madeafter repeating a series of phases for several times. This method ispreferable when the flow rate is desired to be slowly followed, forexample. Further alternatively, a method may be employed whereby thetransfer pumps 5, 6, and 7 are corrected all at the same time such thatthe feed weight and the removal weight of body fluid coincide, after theend of the entire series of phases. This method is preferable in systemswhere the “removed-water weighing phase” and the “feed weight measuringphase” are alternately repeated. In any of these methods, the timing ofcorrection is not particularly limited and it is only necessary that itis performed outside the second and the fourth phases, in which weighingis carried out.

Thus, there is only one weightmeter employed, and by simply controllingthe rotation of the pumps using the control unit, the removal weight ofbody fluid or the feed weight can be accurately controlled. Thus, inaddition to the accuracy of control, the structure of the apparatus canbe advantageously simplified.

Although the above-described examples involved CHDF, it should beobvious to those skilled in the art that the invention is not limited toCHDF in view of the fact that the apparatus performs CHF when the flowrate of the dialysate transfer pump is set to zero, while it performsCHD when the flow rate of the replacement fluid transfer pump is set tozero. It goes without saying that the blood purifying apparatus of theinvention can also be used for conventional hemodialysis,hemofiltration, and hemodiafiltration, in addition to theabove-described CHDF, CHF, and CHD.

INDUSTRIAL APPLICABILITY

As described above, the invention enables the feed weight to becontrolled with higher accuracy than is possible with conventionaltechnique, not to mention the removal weight of body fluid, which is themost important parameter in patient management. Further, the structureof the apparatus can be simplified. The apparatus of the invention doesnot require frequent weighing and adjustment operations by staff as inthe conventional apparatuses, so that the treatment of the patient canbe continued safely while controlling the body fluid weight of thepatient properly. Another advantage is that the dialysate reservoir unitor the replacement fluid reservoir unit can be exchanged as needed, or,in cases where the filtrate and the dialysis drain fluid are stored intanks, for example, the tanks can be exchanged as needed, withoutdirectly affecting the measurement of the removal weight of body fluidor the feed weight, and without terminating the treatment.

1-8. (canceled)
 9. A blood purifying apparatus comprising a dialysatefeed means, a replacement fluid feed means, a drain means, a bloodpurifying device, and a blood circulation path consisting of a blooddrawing line and a blood retransfusing line, wherein: said dialysatefeed means comprises: a dialysate transfer line of which one end isconnected to said blood purifying device and the other end connected toa dialysate reservoir unit; a dialysate transfer pump disposed in saidline; a dialysate reservoir container connected to a dialysate branchline branching off on an inlet side of said dialysate transfer pump; anda shutoff valve attached to said dialysate transfer line upstream of abranch portion; said replacement fluid feed means comprises: areplacement fluid feeding line of which one end is connected to saidblood retransfusing line and the other end connected to a replacementfluid reservoir unit; a replacement fluid transfer pump disposed in saidline; a replacement fluid reservoir container connected to a replacementfluid branch line branching off on an inlet side of said replacementfluid transfer pump; and a shutoff valve attached to said replacementfluid transfer line upstream of a branch portion; said drain meanscomprises: a drain line of which one end is connected to said bloodpurifying device and the other end opened; a drain transfer pumpdisposed in said line; a drain reservoir container connected to a drainbranch line branching off on an outlet side of said drain transfer pump;and a shutoff valve attached to said drain transfer line downstream of abranch portion, wherein the three reservoir containers are each equippedwith a fluid level sensor, said apparatus further comprising aweightmeter for weighing the said three reservoir containers at once,and a control unit for controlling the opening and closing of saidshutoff valves and the pump flow rate of each of said transfer pumps.10. The blood purifying apparatus according to claim 9, wherein theindividual fluid level sensors detect an upper limit of a fluid in eachof said reservoir containers.
 11. The blood purifying apparatusaccording to claim 9, wherein the fluid level sensor for said drainreservoir container detects a lower limit of a fluid in said drainreservoir container, and the fluid level sensors for said dialysatereservoir container and the replacement fluid reservoir container detectan upper limit of fluids in said dialysate reservoir container and thereplacement fluid reservoir container.
 12. The blood purifying apparatusaccording to claim 9, wherein said control unit 30 performs a removedbody fluid weight measuring phase consisting of: a first phase in whichthe shutoff valves 15, 16, and 17 are opened, whereby said dialysatereservoir container 9 and said replacement fluid reservoir container 10are each filled with a fluid while at the same time a fluid isdischarged from said drain reservoir container 8; and a second phase inwhich said apparatus is controlled with each of said shutoff valves 15,16, and 17 closed, and a change in the total fluid weight in saiddialysate reservoir container 9, said replacement fluid reservoircontainer 10, and said drain reservoir container 8 during the operationof said apparatus is acquired from information provided by saidweightmeter 20 in order to weigh the removal weight of body fluid,wherein said control unit 30 controls the flow rate of at least one ofthe transfer pumps such that a desired water-removed weight can beobtained in said second phase.
 13. The blood purifying apparatusaccording to claim 9, wherein said control unit 30 performs a feedweight measuring phase consisting of: a third phase in which each ofsaid shutoff valves 15, 16, and 17 is opened, whereby said dialysatereservoir container 9 and said replacement fluid reservoir container 10are filled with individual fluids while at the same time a fluid isdischarged from said drain reservoir container 8; and a fourth phase inwhich said apparatus is controlled with only the shutoff valve 15 forsaid dialysate feed means A and the shutoff valve 16 for saidreplacement fluid feed means B closed, and in which a change in thetotal fluid weight in said dialysate reservoir container 9, saidreplacement fluid reservoir container 10, and said drain reservoircontainer 8 is acquired from information provided by said weightmeter 20so as to calculate a feed weight which is the sum of the weight ofreplacement fluid and the weight of the dialysate, wherein said controlunit 30 controls the flow rate of the dialysate transfer pump and thereplacement fluid transfer pump such that a desired feed weight can beobtained during the fourth phase.
 14. The blood purifying apparatusaccording to claim 12, wherein a flow rate control is performed based onan arbitrary combination of said removed body fluid weight measuringphase and said feed weight measuring phase.
 15. The blood purifyingapparatus according to claim 12, wherein a flow rate control isperformed by alternately repeating said removed body fluid weightmeasuring phase and said feed weight measuring phase.
 16. The bloodpurifying apparatus according to claim 9, wherein said apparatus is of acontinuous and slow type.”
 17. A method of controlling the bloodpurifying apparatus according to claim 9, said method comprisingperforming a removed body fluid weight measuring phase consisting of: afirst phase in which the shutoff valves 15, 16, and 17 are opened,whereby said dialysate reservoir container 9 and said replacement fluidreservoir container 10 are each filled with a fluid while at the sametime a fluid is discharged from said drain reservoir container 8; and asecond phase in which said apparatus is controlled with each of saidshutoff valves 15, 16, and 17 closed, and a change in the total fluidweight in said dialysate reservoir container 9, said replacement fluidreservoir container 10, and said drain reservoir container 8 during theoperation of said apparatus is acquired from information provided bysaid weightmeter 20 in order to weigh the removal weight of body fluid,wherein said control unit 30 controls the flow rate of the transferpumps 6, 7, and 5 such that a desired removal weight of body fluid canbe obtained in said second phase.
 18. A method of controlling the bloodpurifying apparatus according to claim 9, said method comprisingperforming a feed weight measuring phase consisting of: a third phase inwhich each of said shutoff valves 15, 16, and 17 is opened whereby saiddialysate reservoir container 9 and said replacement fluid reservoircontainer 10 are filled with individual fluids while at the same time afluid is discharged from said drain reservoir container 8; and a fourthphase in which said apparatus is controlled with only the shutoff valve15 for said dialysate feed means A and the shutoff valve 16 for saidreplacement fluid feed means B closed, and in which a change in thetotal fluid weight in said dialysate reservoir container 9, saidreplacement fluid reservoir container 10, and said drain reservoircontainer 8 is acquired from information provided by said weightmeter 20so as to calculate a feed weight which is the sum of the weight ofreplacement fluid and the weight of the dialysate, wherein said controlunit 30 controls the flow rate of the dialysate transfer pumps 6, 7, and5 such that a desired feed weight can be obtained during the fourthphase.
 19. A method of controlling the blood purifying apparatusaccording to claim 9, said method comprising an arbitrary combination ofthe control method based on said removed body fluid weight measuringphase according to claim 14 and the control method based on said feedweight measuring phase according to claim
 15. 20. The blood purifyingapparatus control method according to claim 19, said method comprisingalternately repeating the control method based on the removed body fluidweight measuring phase and based on the feed weight measuring phase.